A woman who was talking on the phone to Trayvon Martin moments before he was shot and killed by George Zimmerman acknowledged on the stand today that she does not know whether Zimmerman or Martin started the fatal fight.

The testimony of Rachel Jeantel, 19, was dissected over two days of often testy cross examination by Zimmerman's lawyers in which she was challenged on her assertion that she heard Martin say "get off" just before he was shot.

Zimmerman, 29, is on trial for second degree murder in Martin's death on Feb. 26, 2012. Martin, 17, was unarmed, but Zimmerman mantains he shot the teenager in self defense.

Jeantel, a key prosecution witness in the racially charged trial, testified that she was talking on the phone with Martin when he told her a "creepy ass cracker" was following him. She told defense lawyer Don West that "cracker" is how she referred to white people in her community.

She had testified that she "could hear" Martin say "get off" to Zimmerman, although West said that during a taped interview with the prosecutor before the trial she had said that she "couldn't hear." West suggested that prosecutor Bernie de la Rionda coached her to say she could hear Martin.

Jeantel, 19, put her hands on her head as she listened in court today to the audio of her interview with de la Rionda, but what she said on the tape was not 100 percent clear. After the tape played Jeantel insisted that she said she could hear Martin, but that prosecutor de la Rionda did not understand her.

However, West got Jeantel to acknowledge under oath that she didn't know if Zimmerman or Martin started the fight the night the teen died.

"The last thing you heard was something hitting somebody?" West asked her.

"Trayvon got hit," Jeantel said.

"You don't know that, do you?" the defense lawyer said.

"No sir," she said.

"You don't know that he didn't take his fist and drive it into Zimmerman's face do you?" the lawyer pressed.

"No sir," Jeantel replied.

The combative exchange was part of her nearly seven hours of testimony over two days. She started the day appearing subdued. Her demeanor was so different from the hostile tone she had towards Zimmerman's lawyer on Wednesday that West asked Jeantel, "You seem so different from yesterday. I'm just checking, did someone talk to last night about your demeanor in court?"

In a painfully embarrassing moment, Jeantel was forced to admit that she did not write a letter that was sent to Martin's mother describing what she allegedly heard on a phone call with Martin moments before he was shot. It came when West asked her to read the letter aloud in court.

"Are you able to read that at all?" West asked.

Jeantel, head bowed, eyes averted whispered into the court microphone, "Some but not all. I don't read cursive."

It sent a hush through the packed courtroom.

She was unable to read any of the letter save for her name, date and the words "thank you."

Jeantel said that she dictated the letter to someone who wrote it for her. West then proceeded to grill Jeantel over why she wasn't specific with Martin's mother about some of the things she heard over the phone, suggesting that her version of what she heard on the phone that night was not complete.

The testimony was an attempt to raise questions about veracity of Jeantel's testimony, who is a key prosecution witness in the racially charged case.

Take an interactive look at the timeline of events surrounding Trayvon Martin's death and George Zimmerman's trial.

Rachel Jeantel was the last person to speak on the phone with Martin moments before he was shot to death by Zimmerman on Feb. 26, 2012.

During cross examination today, Jeantel also testified that when she was interviewed under oath on April 2 by prosecutor Bernie de la Rionda she was sitting next to Trayvon Martin's mother and that influenced what she told the prosecutor.

"You certainly didn't want to say anything that you thought would hurt her feelings or make her grieve even worse," asked West.

"Yes sir," she responded.

"So because of that you were sensitive to (Martin's mother) Mrs. Fulton's feelings when you answered Mr. De la Rionda questions."

"Yes sir," she replied.

"And that's why you cleaned up some of the language that Trayvon Martin used?" West asked.

"Yes sir," she responded.

During nearly two hours of cross examination Wednesday in which he tried to raise questions about her version of events and accused her of telling several lies under oath, including about her whereabouts during Martin's wake.

"Under oath, you created a lie and said you went to the hospital?" asked West.

"Yes," responded Jeantel. She said she lied because she didn't want to see the body.

Jeantel became increasingly agitated and scoffed when West told her that she would have to continue testifying.

She is seen as a critical witness to the prosecution because she is the only person able to say that Martin claimed that he noticed a strange man following him and that he was scared. Jeantel said Martin described the stranger as a "creepy ass cracker."

Jeantel said Martin, 17, was walking home during halftime of the NBA All-Star Game when he became unnerved because he was being followed.

"He told me the man kept following him," Jeantel said.

Jeantel said she told Martin to run, but that he responded that he was almost home.

"I say, 'Trayvon,' and then he said, 'Why are you following me for?'" Jeantel testified. "And then I heard a hard-breathing man come say, 'What you doing around here?' ... And then I was calling, 'Trayvon, Trayvon.' And then I started to hear a little bit of Trayvon saying, 'Get off, get off.'"

At times during her early testimony with the prosecution, Jeantel dabbed away tears.

During cross-examination, defense attorney Don West tried to dig into the chain of events preceding Martin's death. West asked why Jeantel didn't call law enforcement after the phone died.

"I thought he was going to be OK because he was right by his daddy's house, but his daddy was not home," Jeantel said as Martin's father cried in court.

Tracey Martin eventually reached out to Jeantel after looking at his son's phone log, Jeantel said. She added that she expected law enforcement to reach out to her, but none did, apparently, until the Florida Department of Law Enforcement contacted her much later.

Zimmerman, said he was defending himself from Martin after the unarmed teenager allegedly confronted him, knocked him down and banged his head of the sidewalk. Prosecutors allege that the former neighborhood watch captain profiled and followed the teenager before killing him.